Typically, video data includes a large amount of data. Therefore, an apparatus that handles the video data encodes and compresses the video data in order to transmit the video data to other apparatus or to store the video data in a storage device. Advanced video coding (MPEG-4 AVC/ITU-H H.264) and high efficiency video coding (HEVC/ITU-T H.265) were developed as typical video coding standards.
In such coding standards, a picture to be encoded is divided into a plurality of blocks. A prediction block is generated for each block to be encoded from another encoded picture or an encoded region of the picture to be encoded. Quantization of orthogonal transform coefficients that are obtained by performing orthogonal transformation on prediction error signals between the block to be encoded and the prediction block achieves compression of an information volume.
The image quality of a reproduced picture that is obtained by decoding the encoded picture data, however, is deteriorated by the quantization of the orthogonal transform coefficients, as compared with the image quality of the original picture. Therefore, a deblocking filter has been adopted since MPEG-4 AVC, as an in-loop filter to suppress deterioration caused by the quantization of the orthogonal transform coefficients. Further, quantization may cause artifacts that are referred to as mosquito distortion, near the edge of an object in the picture. Accordingly, in HEVC, a sample adaptive offset (SAO) filter that is a type of adaptive filter is adopted as the in-loop filter, in addition to the deblocking filter (for example, see Japanese Unexamined Patent Publication (Kokai) No. 2015-104061, and ISO/IEC 23008-2:2015 Information technology—High efficiency coding and media delivery in heterogeneous environments—Part 2: High efficiency video coding, 2015).